Voice-over-Internet Protocol (VoIP) is a technology for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Cloud communications are Internet-based voice and data communications where telecommunications applications, switching and storage are hosted by a third-party outside of the organization using them, and they are accessed over the public Internet.
Both of these technologies may implement their respective communications using the Session Initiation Protocol (SIP). The Session Initiation Protocol is a communications protocol for signaling for the purpose of controlling multimedia communication sessions. Generally, the Session Initiation Protocol operates above the Transport Layer of the Open Systems Interconnection Model, and therefore, does not communicate information maintained at, for example, the Transport layer.
Certificate authentication is a system utilizing a public key certificate that is used to authenticate devices and organizations by proving their ownership of a public key derived from a mutually trusted source. Generally, certificate authentication is implemented at the Transport Layer of the Open Systems Interconnection Model through, for example, the Transport Layer Security (TLS) protocol.